There has been proposed a laser display device incorporated with a laser light source for emitting laser light of three colors of RGB (red, green, and blue). Since laser light has monochromaticity, and is capable of expressing colors in a wide range, a laser display device incorporated with a laser light source is capable of displaying colorful images. A laser light source for emitting laser light of several watts is necessary to realize a large-screen laser display device by laser light of three colors of RGB. There has been used a gas laser such as a high-output Ar laser or Kr laser, as means for realizing the laser light source. These gas lasers, however, have a very low energy conversion efficiency of about 0.1%. Accordingly, a large-sized device including a cooling device has been required.
As means for solving the above problem, there has been considered a technology of generating short wavelength light by a solid-state laser. It has been possible to generate high-output green light by subjecting light of 1.064 μm which has been generated from a solid-state laser such as an YAG laser to wavelength conversion into a second harmonic by a wavelength conversion element. Further, in recent years, there has been reported generation of high-output green light using a Yb-doped fiber laser. For instance, non-patent literature 1 discloses generation of green light of 60 W by using an LBO as a non-linear optical element.
Further, there has been proposed a method of using green light or blue light which is directly generated from a solid-state laser, as a light source. For instance, patent literature 1 proposes a method, wherein red light and green light are generated by exciting a laser medium doped with a trivalent praseodymium ion (Pr3+) by laser light emitted from a GaN-based semiconductor laser, and the red light and the green light are applied to a laser display.
However, in the aforementioned laser light source, it is difficult to modulate the intensity with high efficiency, which is required in a light source for a laser display device. In particular, in non-patent literature 1 and patent literature 1, there is no consideration and proposal about an arrangement of efficiently using both of pump light and laser light, as a light source for a laser display device.
Non-patent literature 1: Anping Liu, Marc A. Norsen, Roy D. Mead, “60-W green output by frequency doubling of a polarized Yb-doped fiber laser”, Optics Letters vol. 30 No. 1, Jan. 1, 2005, p. 67-69
Patent literature 1: JP 2001-264662A